President Yoweri Museveni paused for breath on a path in the middle of the Bwindi Impenetrable Forest as a waiter hurried forward carrying a tin of glucose powder. The 56-year-old head of Uganda carefully took a mouthful before offering the tin to his panting aides, who were bringing up the rear of the 35-person entourage.

Dressed in a military uniform bearing his general's pips, the president steadily made his way through the cultivated hills and into the dense forest, where his trackers eventually located a small group of gorillas eating red fruit and rolling on their backs. The silverback, the big male in charge of the group, glared angrily out of the bushes at the intruders. Museveni watched for five minutes, then turned away and went to sit on a drinks cooler that the waiter had stoically carried up the steep forest track.

The president had invited me to accompany him on the trek marking the anniversary of the death of eight foreign tourists and one Ugandan park warden at the hands of Rwandan Hutu rebels. The attack attracted international media attention and caused Uganda's tourism industry to collapse. The president wanted to show the world that the area was now safe for tourists to return.

Bwindi is in a ravishing part of western Uganda. As the presidential helicopter flew south from Kampala, the land began to crumple into tight green hills. The earth is intensely cultivated with small, rectangular mud houses positioned neatly in the middle of fields of banana trees. On the horizon was a faint blue haze where Uganda blended into Congo.

The first hour of the trek was through slopes of coffee and banana plantations. The forest began suddenly at the crest of a hill, and plunged into a valley before stretching off on rolling hills into Congo. We stayed at the crest of the hill for an hour while the trackers tried to locate the gorillas. Mountain gorillas normally don't move more than two kilometres in a day and once the trackers, many of whom are former poachers, have located their nests, they follow their trail of droppings and half-eaten fruit and foliage.

Unfortunately, our gorillas had moved two kilometres up the side of another hill, which meant there was a long slog still ahead.We slipped down a muddy slope and there in front of us were two gorillas, with dense, black, glossy fur. They came slowly out of the bush, without fear. Then they climbed a tree directly in front of us and started eating the red fruit.

The guides began identifying the animals and making gorilla noises to attract their attention. I was more interested in watching the president who said he liked the forest more than the gorillas.

In truth, wildlife viewing is not a very Ugandan enterprise. The people who live around the park in Bwindi tend to look upon gorillas as at worst crop-raiding vermin - they steal bananas - at best a potential form of income: gorilla tourism is arranged so that 12% of permit revenue goes towards building schools and roads in the region, thereby giving locals an incentive not to encroach on or poach in the forest.

Before we left, the guides managed to locate more gorillas further down the slope. A baby was playing with his toes and rocking back and forth, a young male and female tussled with each other, the male suddenly giving a not very threatening chest pound.

All the time, the silverback sat at the back watching us, his face impassive but his eyes boring through. He was standing guard against potential threat and I felt like an intruder.

Out of the mist - the protection of a species

Dian Fossey was wrong when she wrote in Gorillas In The Mist in 1983: "Human beings must decide now whether or not the Mountain Gorilla will be a species discovered and extinct within the same century." I have only just returned from both Uganda and Rwanda in the next century. What she underestimated was the extraordinary desire of others to see the gorillas and the global power of the travel industry.

Tourism was Rwanda's third largest revenue source after tea and coffee before the genocidal war started in 1994, the vast majority of it focused on one animal, the mountain gorilla. So, too, in Uganda, which after bravely coming back from the Idi Amin and Milton Obote dictatorships, suddenly lost its tourism industry in March last year after the massacre. In today's world of "rebel guerillas", there can be few better ways to harm a country than killing some tourists within it.

For Uganda, those poor victims, caught in a conflict not of their making, unwittingly cost the country tens of millions of dollars, shook the whole gorilla conservation programme, put hundreds of people out of irreplaceable jobs and nearly bankrupt the Uganda Wildlife Service.

For the crux of it is that a gorilla-tracking permit had made saving gorillas an economic necessity for Rwanda and Uganda. Just three habituated gorilla groups of about 38 individuals in total could generate over US$3m in revenue a year, making each individual worth nearly US$90,000 a year to Uganda. In fact, the permit fees had in past years allowed for vast swathes of both countries to be preserved, even if few people even saw these other wildlands. It was, and still is, a tourism success story.

Apart from preserving these lands for rich foreigners to enjoy, other less obvious but no less tangible benefits have been extended to the locals. For forests and mountains are the very basis of our natural life support processes. Their worth as water suppliers, water purification services, medicine chests and food sources in a country that can't afford the most basic services is incalculable.

Travel to Uganda or Rwanda today and you will see how much they value mountain gorillas. Whole army brigades are garrisoned around parks, squadrons of AK47-wielding soldiers escort you gorilla-tracking in the mountains and Russian tanks point their guns menacingly into impenetrable jungle. Only a few years ago, such security to protect a few furry animals would have been inconceivable, but today it is as essential as protecting a major oil refinery.

At last the vital economics of conservation have started working and for those of us privileged enough to be able to travel to such places, what is the price of a permit for an experience unlike any other will have - in the natural world at least.

Encounter (020 7370 6845) organises 6 night gorilla safaris. Travle is in small groups, accompanied by experienced local guides. An hour is spent in close quarters with the animals in their natural habitat. The cost is £295, excluding flights, plus the cost of a gorilla permit, payable locally at an approximate cost of £154. Camping accomodation, food and guides are all included. Return flights to Kampala can be arranged from £500. Departure dates July 10, August 14, September 18, October 23 and November 27. Discovery Initiatives (020 7924 5696) has 15 day trips taking in Kampala and national parks and forests in Uganda and Rwanda. It includes four separate opportunities to view gorillas. Prices are from £3150 per person, including international flights, all accomodation, meals, park fees, transport, leader and guides and two gorilla permits. Departure September 3.